The invention herein concerns antibodies directed against different receptors of interferon gamma on human cells. Such antibodies can block the action of interferon gamma on some cells and not on others, thus leading to selective action of interferon gamma as a pharmaceutical agent or to prevention of the action of endogenous interferon gamma on some cells and not on others.
Interferon gamma is a lymphokine produced by activated T-lymphocytes and exerting many immunoregulatory activities. It is generally known as an immune stimulant because of its ability to activate monocytes and macrophages towards cell killing in vitro (Le et al., 1983, J. Immunol. 131, 2821-2823).
In addition, interferon gamma is a direct inducer of class I and II major histocompatibility complex (MHC) antigens in both immune and non-immune cells (Steeg et al., 1982 J. Exp. Med. 156, 1780; Wallach et al., 1982 Nature 299, 833-836). So far, it is the only known direct inducer of class II MHC antigens and it exerts its effect even at very low concentrations (1-10 pM).
Class II major histocompatibility antigens (HLA-DR in humans) play a major roll in the immune system. These transmembranal proteins are mainly expressed on monocytes, macrophages, B lymphocytes, langerhans cells and thymus epithelial cells. They are absent from most tissue specific cells and from resting T cells. The genes of these proteins show extensive polymorphism which results in a large number of different serotypes.
In general, T-lymphocytes respond to a given antigen only when it is presented on the surface of an "antigen presenting cell" such as monocytes and in combination with class II major histocompatibility antigens such as HLA-DR in humans and Ia in mice. Once this occurs, an antigen specific clonal expansion of T helper cells will take place. These T cells will induce cytotoxic/suppressor T cells on one hand and will "help" B cells to mature and become antibody producing plasma cells. Another important function of HLA-DR is in the interaction of T cells with B cells which is essential for proliferation and maturation of B cells. Further details on the role of HLA-DR are found in immunology textbooks (e.g. The Immune System by I. McConnell, A. Munro and M. Waldman, Blackwell Scientific Publications, 1981, Oxford). Thus interferon gamma, plays a central role in the intitiation of the immune response by modulating the level of surface HLA-DR on antigen presenting cells and it plays an important role in augmenting cellular cytotoxicity.
Additional studies have shown that the induction of HLA-DR by interferon gamma is not limited to hematopoietic cells. In fact many types of cells including fibroblasts, endothelial cells, keratinocytes, astrocytes and thyroid follicular cells will express HLA-DR after exposure to low doses of interferon gamma in vitro.
As to the role of HLA-DR in non-hematopoietic cells there is a debate among various investigators. Thus, Mason and Barclay (Immunobiology 168, 167-171, 1984) pointed out that Ia positive cells (Ia is the mouse equivalent of human HLA-DR) are also producing interleukin-1 and therefore can be suitable as antigen presenting cells. They specifically referred to vascular endothelial cells (Hirshberg et al., 1980, J. Exp. Med. 152, 2495), keratinocytes (Luger et al., 1982, J. Immunol. 128, 2147) and astrocytes (Fontana et al., 1982, J. Immunol. 129, 2143). In all of these cases, T cell proliferation which was taken as a measure of immune stimulation was induced by these Ia positive, non-hematopoietic cells. More recently, Bottazzo et al., (Lancet 1983, II, 1115; Immunol. Today 5, 23, 1984) proposed that the expression of HLA-DR on thyroid follicular cells may be involved in the initiation and maintenance of autoimmune dieases of the thyroid gland. Later (Londei et al., Science 228, 85, 1985) they identified T-cell clones which originated from autoimmune thyroid glands and recognized autologous HLA-DR positive thyroid cells. These authors suggested that autoimmune thyrocytes "may act as antigen presenting cells that present their own surface autoantigens". In another study, Fierz et al., (J. Immunol. 134, 3785-3793, 1985) demonstrated that interferon gamma treated astrocytes are Ia positive and that such treatment augments up to four-fold the induction of T-cell proliferation by contact with said astrocytes. These authors state that it is conceivable that "abnormal" induction of Ia antigens on astrocytes by some stimulus is a basis for the development of an autoimmune disease in the central nervous system. While the above studies were performed in vitro, a recent in vivo study was performed by Groenewegen et al., (Nature 316, 361-363, 1985). Using cyclosporin A, a known inhibitor of interferon gamma production, they have demonstrated that class II antigen expression by canine endothelial cells was not constitutive but rather it was interferon gamma dependent. These authors also suggested that class II MHC products (e.g., HLA-DR in humans and Ia in murine cells) of non-hematopoietic cells are involved in immune responses.
The conclusion of the aforesaid studies was mainly circumstantial and based only on cell to cell interaction and T-cell proliferation. However, in none of the cases reported so far, direct cytotoxicity of T-cells against HLA-DR bearing tissue cells or induction of specific autoantibodies was reported. These thoughts were expressed recently by Mowat (Lancet, Aug. 3, 1985, p. 283) who suggested that "enhanced expression of class II MHC antigens in autoimmune disease merely reflects the involvement of effector T-lymphocytes in the tissue pathology" and although he did not dismiss the role of HLA-DR in worsening autodestructive processes, he suggests a careful experimental considersation.
Three unrelated lines of research indicate, in an indirect way, that in fact the situation may even be opposite to what was so far expected, namely, it is possible that interferon gamma actually inhibits immune response by inducing HLA-DR on non-hematopoietic cells. Taramelli et al. (Int. J. Cancer 34, 797-806, 1984) studied the role of HLA-DR on metastatic human melanoma cells in suppressing autologous lymphocyte mediated cytotoxicity and lymphocyte proliferation. Human tumor cells can stiumlate in 60-70% of the cases the proliferation of autologous lymphocytes and their differentiation into tumor specific cytotoxic T-cells. This is effected via production of IL-2. Taramelli et al., found that metastatic melanoma cells (from lymph nodes) can inhibit the IL-2 dependent stimulation of autologous lymphocytes. This inhibition was observed only with HLA-DR positive melanoma cells. Moreover, on treatment of HLA-DR negative cells with interferon gamma they became HLA-DR positive and acquired the suppressive activity. Thus, the induction of HLA-DR on melanoma cells by interferon gamma was circumstantially linked to inhibition of an autologous lymphocyte mediated cytotoxicity. If this phenomenon is not limited to neoplastic cells but rather it occurs in all cells, then the appearance of HLA-DR on tissue cells associated with an autoimmune disease maybe a part of the homeostatic response which inhibits tissue damage by monocytes, killer cells and cytotoxic T-lymphocytes. Indeed, recently it was reported by Biogen Inc., that cancer patients who suffered from rheumatoid arthritis and were given interferon gamma as a potential antineoplastic drug showed signs of improvement in their arthritis. In a preliminary study, 70% of the patients experienced relief from their pain and swelling. These observations may be related to an enhanced expression of HLA-DR on sinovial cells as was demonstrated in vitro.
The best documented role of interferon gamma as a suppressor of cell mediated cytotoxicity is in the field of natural killer (NK) activity. Several studies have demonstrated that while interferon activates NK cells towards killing of target cells it also renders these target cells more resistant to NK (Trincieri and Santoli, 1978, J. Exp. Med. 147, 1314; Hansson et al., 1980, J. Immunol. 125, 2225; Welsh 1981, Antiviral Res., 1, 5; Wallach 1982, J. Interferon Res. 2, 329; Wallach 1983, Cellular Immunol. 75, 390). It appears therefore that interferon gamma may have opposing effects on different cells. Monocytes and NK cells are activated by interferon gamma and became more efficient in their function as cytotoxic cells, while various non-hematopoietic cells which are potential targets for lysis may become NK resistant. Moreover, certain tumor cells (metastatic melanoma, Taramelli et al., Int. J. Cancer 34, 797, 1984; murine leukemia, Ramila and Erb, Nature 304, 442, 1983; glyomas, Gately et al., Acta Neurochirurg. 64, 175, 1982; and lyposarcoma, Roth et al., J. Immunol. 130, 303, 1983), have immunosuppressive activity which is possibly linked with the expression of HLA-DR on their surface.